Effects of high temperature on the resting membrane potential and the excitatory postsynaptic potential in hippocampal CA1 neurons

We examined the effects of temperature increase on the resting membrane potential (RMP) and the excitatory postsynaptic potential (EPSP) evoked by stimulation of Schaffer collaterals in rat hippocampal CA1 neurons in vitro. The temperature of the external solution of the rat hippocampal slice was initially kept at 36°C for 30min. The mean RMP was -67.4±1.2mV (n=13) at 36°C. The increase of the temperature from 36 to 40°C for 5∼8 min produced a membrane hyperpolarization (3.2±0.8mV, n=8) associated with a decrease in input resistance. After returning the temperature to 36°C for 20min, the RMP recovered. The EPSP was reversibly depressed to 40% of the control by the temperature increase from 36 to 40°C for 5∼8 min. Consecutive exposure of high temperature (40°C) hyperpolarized neurons more promptly than that obtained by the first exposure to 40°C, and also depressed the EPSP. When the temperature was maintained at 40°C, a rapid and large depolarization to nearly 0mV occurred in about 50∼90 min. A rapid and large depolarization was produced within 10min by the temperature increase from 36 to 42°C. The EPSP was completely depressed immediately with the onset of the large depolarization. The RMP and the EPSP hardly recovered by returning the temperature to 36°C, after the onset of the large depolarization. These results suggest that high temperature rapidly depresses the excitatory synaptic transmission and that long-lasting high temperature may insult the membrane structures of CA1 neurons by an unknown mechanism. [Jpn J Physiol 55 Suppl:S150 (2005)]